1. Field
The present disclosure relates to tires for civil engineering vehicles and more particularly to tires having treads having high thicknesses (“extra deep tread”) and intended to equip vehicles employed in underground mines.
2. Description of Related Art
Works Vehicles used in underground mines, which are dark by nature, are equipped with tires whose treads are without any tread pattern. These tires roll along particularly hostile tracks and have a wear of their treads which must be able to be monitored to avoid any incident which would require difficult intervention resulting in mining being stopped.
The tires concerned here comprise treads having very high thicknesses of material to be worn; very high thicknesses are intended to mean here a thickness which is at least equal to 70 mm and can range up to 130 mm or even more.
Custom has resulted in the presence of at least one transverse notch in these treads so as to allow the wear of the tread to be monitored. These transverse notches are formed when molding the tire and open both onto the rolling surface of the tread and onto one of the lateral faces of this tread.
This wear-monitoring device makes it possible to carry out visually an evaluation of the remaining notch depth, but this is only an indicative evaluation of the remaining thickness. This same wear-monitoring device is not completely satisfactory since it is necessary, in order to know the remaining thickness, to carry out a measurement of the remaining depth of the notch with a suitable apparatus.
Moreover, each notch opening onto the rolling surface in the new state is a possible entry point of foreign bodies which may be found on the running tracks in the mines. These foreign bodies may then damage the tire or even promote tear-off of material and then disturb the reading of the remaining depth of material to be worn.
Moreover, it is known, see in particular GB-2312654-A, to form a tread by superposing two layers of different colors, the appearance of the second layer indicating a predetermined wear level.
Definitions:
Equatorial median plane: this is a plane perpendicular to the axis of rotation and passing through the points of the tire radially furthermost from the said axis.
Radial direction is intended to mean in the present document a direction which is perpendicular to the axis of rotation of the tire (this direction corresponds to the direction of the thickness of the tread).
Transverse or axial direction is intended to mean a direction parallel to the axis of rotation of the tire.
Circumferential direction is intended to mean a direction which is tangent to any circle centred on the axis of rotation. This direction is perpendicular both to the axial direction and to a radial direction.
The total thickness E of a tread is measured, on the equatorial plane of the tire provided with this tread, between the rolling surface in the new state and the radially outermost part of the crown reinforcement in the new state.
The usual tire rolling conditions or use conditions are those which are defined by the standard E.T.R.T.O. or by the standard T.R.A.; these use conditions stipulate the reference inflation pressure corresponding to the load capacity of the tire indicated by its load index and its speed code. These use conditions may also be termed “nominal conditions” or “usage conditions”.